1. Field of the Invention
The present invention relates to an electron microscope and, more particularly, to an electron microscope permitting one to observe the reaction process of a specimen under certain ambient conditions. The invention can be applied to transmission scanning electron microscopes, transmission electron microscopes, and scanning electron microscopes.
2. Description of Related Art
In the field of electron microscope imaging technology, numerous techniques for imaging specimens and their surroundings under non-vacuum ambients have been already disclosed. Their purpose is to elucidate the mechanism of a reaction, for example, between a gas and a solid by observing and analyzing the reaction process with an electron microscope at an atomic level. Up to now, there are reports in which the mechanism of a reaction between a gas and a solid or between a liquid and a solid has been clarified by the above-described method.
For example, a technique for controlling the ambient around a specimen by incorporating a gas inlet mechanism and a gas tube extending close to the specimen into a specimen holder for an electron microscope and supplying an arbitrary gas into the gas tube such that the gas is introduced through the gas inlet mechanism is disclosed (see, for example, JP-A-2003-187735 (paragraphs 0023-0031; FIG. 1)). The specimen holder has a grip in which a connector for gas introduction is mounted. A gas pipe extends from the grip to the vicinity of a specimen stage on which the specimen is set. Gas can be introduced close to the specimen through the gas pipe in the holder via the gas introduction connector of the grip. Accordingly, the reaction process between a gas and a solid can be observed with the electron microscope while the gas is flowing. This contributes to elucidation of the mechanism of the reaction between the solid and gas.
However, if the above-described technique is used alone, the pressure in the vicinity of the specimen chamber can be increased only up to about 10−3 Pa to 10−5 Pa. In this case, if the reaction process between a gas and a solid is observed and fundamental knowledge should be obtained, then satisfactory results would be obtained. However, it is expected by the industrial world that the mechanism of the process between a gas and a solid in an atmosphere closer to atmospheric will be elucidated. Hence, it is desired that a breakthrough will be made in this technical field.
According to a conventional technique different from the aforementioned technique, the pressure around the specimen chamber can be increased nearly up to the atmospheric pressure by optimizing the gas flow rate. However, if the specimen holder is inserted into a general-purpose electron microscope and gas is supplied until the pressure in the vicinity of the specimen chamber is increased to the atmospheric pressure, then the pressure is increased even up to the electron beam source including acceleration tubes. This creates the possibility that electrical discharge is caused, damaging the microscope. Furthermore, pressure increase in the vicinity of the optical axis leads to a decrease in the penetrative power of the electron beam or to a deterioration of the resolution. In addition, the critical pressure at which electrical discharge in the electron beam source occurs, the penetrative power of the electron beam, and resolution differ according to gas species. In this way, the electron microscope fails to cope with various conditions sufficiently. Consequently, imaging of the process of the reaction between a gas and a solid in an almost actual environment (e.g., in the atmospheric condition) has not been substantially accomplished.